There are many applications in science, medicine, defense, and industry where imaging far-infrared (FIR) to mid-infrared (MIR) wavelengths of light is desirable. These applications include medical imaging, firefighting, homeland security, monitoring volcano activities, infrared astronomy, national and tactical missile defense, and monitoring heat emission in certain geological areas. In medicine, high thermal resolution is an essential requirement for medical imaging. For example, cancer cells have higher metabolic activity than surrounding tissue, so an imaging system that can detect minute changes in temperature of cancer cells relative to surrounding tissue is highly desirable. In astronomy, visible light from distant objects can be absorbed by dust or other elements and compounds such as ozone in the Earth's atmosphere, but FIR and near-infrared (NIR) light from these same sources would penetrate the atmosphere (about a 9.5-10.5 μm window). In missile defense systems, warm targets with low background irradiance can be resolved at FIR and MIR wavelengths.
Existing techniques for detecting FIR and MIR wavelengths have many drawbacks. The technology of FIR and MIR detecting cameras is about 20 years behind standard common visible and near NIR cameras, particularly digital cameras. NIR cameras have resolutions beyond the single megapixel range (e.g., 1024×1024 pixels), while comparable and more expensive FIR and MIR cameras have resolutions only around 240×240 pixels. Another type of detector is a thermal detector, which operates on the principle that when the thermal detector is heated by incoming infrared radiation, the temperature of the thermal detector increases and the temperature changes are measured by any temperature-dependent mechanism such as thermoelectric voltage, resistance, and pyroelectric voltage. Unfortunately, detection systems dependent directly on temperature changes have slow response times.
A quantum electronic technique for MIR and FIR detection employs a Quantum Well Infrared Photodetector (QWIP), which relies on measuring currents arising from electrons in the conduction level of a quantum well becoming free of their confined quantum states. This technique suffers from the need to cool the QWIP to cryogenic temperatures so that thermal currents do not swamp out the optically-generated currents. In addition, because an electrical current is being measured, the manufacturing process requires the step of adding electrical wiring to the semiconductor wafer.